1. Field of the Invention
This invention relates to drainfields and, in particular, this invention relates to a process for renovating failed septic tank soil absorption systems or maintaining functioning septic tank soil absorption systems.
2. Background
A typical on-site septic system is disclosed in FIGS. 1-3 generally at 20 and includes a hydraulic system 21 and an absorption field 22. Sewage is generated from a facility, such as a house 23, and flows through a sewer line 24 into a settling tank, such as a septic tank 26. Upon being conveyed to the septic tank 26, solid materials are allowed to settle out of the sewage and the separated liquid effluent (wastewater) then flows through line 28 to the absorption field 22 via a system designated generally at 30.
The system 30 depicted in FIG. 1 is a trench system and will be more particularly described hereinbelow. However, the present method is contemplated to be applicable to bed systems, seepage pits, mound systems, or any other system using an underlying soil profile to absorb and detoxify wastewater. These and other disposal systems are disclosed in Onsite Wastewater Treatment and Disposal Systems, Design Manual No. 35, U.S.E.P.A. (January 1980), hereby incorporated by reference Each of these disposal systems uses an absorption field defined in a soil profile to dispose and purify wastewater. While the following discussion addresses primarily a trench system, the problem of maintaining and reclaiming soil absorption systems is common to each method of wastewater disposal and the present
The trench system depicted in FIGS. 1-3 includes distribution boxes 32, 34, and 36, lines 38 and 40, and laterals 42, 44, 46, 48, 50, and 52. Wastewater is conveyed from the septic tank 26 through the line 28 to the distribution box 32. The distribution box 32 usually divides wastewater flowing therein between the laterals 42 and 48 and the line 38. The line 38 conveys wastewater to the distribution box 34. The distribution box 34 divides the wastewater flowing therein between the laterals 44 and 50 and the line 40. The wastewater flowing through the line 40 flows into the distribution box 36, where the waste water is divided between laterals 46 and 52. Each of the distribution boxes 32, 34, and 36 may include valves or the like to further control the flow and distribution of wastewater. For instance, the distribution box 34 could contain a valve controlling the flow or the amount of flow, to the laterals 44 and 50, as well as the line 40.
The entire disposal system 20 is usually buried. However, for the sake of clarity, the absorption system 30 is shown as being buried within a trench system 54. With the exception of the permeable laterals 42, 44, 46, 48, 50, and 52, the entire disposal system is usually impermeable to fluid egress. The laterals usually contain perforations or other openings to allow egress of wastewater into the soil profile.
Referring to FIGS. 4 and 5, the exemplary trench system 54 is present within a soil profile 60. The soil profile 60 may arbitrarily be considered to include an upper portion 62 and a lower portion 64. A trench 66 is excavated in the soil profile 60 and is defined by sidewalls 68 and 70 and a bottom 72. The sidewalls 68 and 70 are defined by the upper soil profile portion 62 and the bottom is defined by the lower soil portion 64. As can be seen, one of the laterals 52 has been installed within the trench 66. A multiplicity of perforations 76 for wastewater egress can be seen in the lateral 52. A layer 80 of aggregate, such as gravel, is laid in the trench 66 so as to more or less evenly cover the bottom 72 to a desired height (e.g., four inches). The lateral 52 is then laid atop the gravel layer 80 and another gravel layer 82 is poured in to cover the lateral 52 to a desired height (e.g., six inches). A usually semi-permeable barrier 84 covers the gravel layer 82 and backfill 86 is used to fill the remainder of the trench 66. The barrier 84 prevents the backfill from penetrating, and plugging, the gravel layers 80 and 82 and may also shed moisture percolating down from the surface of the soil profile 60. Shedding moisture thusly may be desirable to prevent the gravel layers 80 and 82 from being filled by water percolating from the surface. Wastewater egresses the lateral 52 via the perforations 76 and enters the interstitial spaces between the gravel particulates in layers 80 and 82. From the layers 80 and 82, the wastewater enters the soil profile 60 by being absorbed through an infiltrative surface 87 formed by the sidewalls 68 and 70 and bottom 72. The direction of the wastewater flow through the soil profile 60 is generally down as indicated by arrows 88, but may be somewhat lateral as depicted by arrow 90. The texture and water content are two major factors determining the extent and direction of the travel of the wastewater entering the soil profile 60. Upon entering the soil profile 60, the wastewater is exposed primarily to bacteria disposed on the surface of the soil particulates. These bacteria detoxify the wastewater by decomposing undesirable compounds dissolved or suspended therein. When the portion of the soil profile 60 surrounding the trench 66 becomes saturated with wastewater, wastewater pools within the gravel layers 80 and 82 until soil conditions allow for wastewater entry and percolation.
Initially, wastewater flows relatively freely into the soil profile 60. However over time, the soil profile 60 loses the ability to absorb the wastewater. When the hydraulic loading rate of the system exceeds the wastewater infiltration of the soil profile, the wastewater begins to pond, or accumulate, in the system. If this situation continues, the net result is wastewater backing up into the home or appearing the above the ground surface above the absorption field 30. In either event, the septic system is considered to have failed. Remedies for restoring absorption fields which will no longer absorb sufficient amounts of wastewater include discontinuing use of the system, use of hydrogen peroxide or other oxidizing agents such as ozone in the disposal field, reduction of the BOD of effluent leaving the settling tank, or installing a new absorption field. Moreover, maintaining the equipment necessary to produce hydrogen peroxide or ozone can be time consuming and costly as well. Discontinuing use of septic systems is usually not feasible. Moreover, applying hydrogen peroxide or other oxidizing agents to the soil profile has often not renovated the system and has been observed to be deleterious to the soil structure. Reducing BOD and suspended solids in wastewater being conveyed to an absorption field is frequently expensive and requires continual monitoring and maintenance.
While not desiring to be limited to any particular theory, a layer called a biological mat or biomat 94 (FIG. 5) forms proximate the soil infiltrative surface (i.e., proximate sidewalls 68 and 70 and bottom 72). The biomat may be anaerobic residues as well as undecomposed solids from wastewater, bacteria, and bacterial extracelluar polymers which clog the soil pores within the biomat layer 94. Due to the lack of available oxygen, an almost exclusively anaerobic environment is created within the portion of the soil profile 60 being infiltrated by wastewater, especially so proximate where the biomat layer 94 forms. A nonlimiting listing of anaerobic microbes often present in soil include bacterial genera Sphaerotilus, Pseudomonas, Escherichia, Salmonella, Shigella, Klebsiella, Enterobacter, Aeromonas, Desulfovibrio, Clostridium, Streptococcus, and Methanobacterium, and other microbial genera Nocardia and Streptomyces. A nonlimiting listing of aerobic bacterial genera often present in soil includes Rhodospirillum, Chlorobium, Beggiatoa, Flexibacter, Thiothrix, Nitrosomonas, Nitrobacter, Thiobacillus, and Bacillus. In contrast to anaerobic bacteria, aerobic bacteria are much more efficient in decomposing organic matter within the effluent, whether the organic matter is dissolved in the water or present as suspended solids. Therefore, delivery of dissolved oxygen via wastewater, may be useful in promoting aerobic activity and restoring the hydraulic conductivity within failed or failing absorption field systems.
There is then a need for a system to both maintain and rehabilitate an absorption field. There is a particular need for a system to maintain and restore an absorption field without reducing the BOD of effluent being conveyed to the absorption field.
The present invention substantially meets the aforementioned needs of the art by providing an absorption field reclamation and maintenance system. The absorption field reclamation and maintenance system of this invention restores and/or maintains absorption fields without reducing the BOD of effluent (wastewater) being conveyed to the absorption field.
It is therefore an object of this invention, to provide a wastewater disposal system, the wastewater disposal system including a hydraulic system and an absorption field. The hydraulic system conveying wastewater effluent from a facility (e.g., a residence) to an absorption field. The hydraulic system may include an anaerobic portion and aerobic portion, the anaerobic portion with an anaerobic BOD, the aerobic portion with an anaerobic BOD, the anaerobic BOD substantially equal to the aerobic BOD. In some embodiments, the aerobic BOD may be at least 90 percent, 95 percent, or 99 percent of the anaerobic BOD. The hydraulic system may include a settling tank, an impermeable fluid conducting member, and a permeable fluid conducting member. The settling tank receives wastewater from the facility. Solids settle from the wastewater and insoluble materials separate from the wastewater in the settling tank. Effluent, separated from the settled solids and insoluble materials, flows from the settling tank to the impermeable fluid conducting member. The permeable fluid conducting member receives effluent from the impermeable fluid conducting member and provides openings for egressing effluent into the absorption field.
The anaerobic portion of the hydraulic system may be disposed in a portion of the settling tank, in the settling tank and a portion of the impermeable fluid conducting member, or in the settling tank and an adjoining portion of the impermeable fluid conducting member. The aerobic portion may be intermittent via a mechanism, such as a timer-actuated aerator, configured and disposed to oxygenate effluent flowing through one of the settling tank and the impermeable member. The oxygenating mechanism may substantially separate the aerobic from the anaerobic portions. The oxygenating system may include an air pump, the air pump may be in fluid communication with the settling tank and/or the impermeable conducting member. The oxygenating mechanism may further include an oxygen sensor to sense a dissolved oxygen concentration in the effluent and to activate an air pump or aerator, when the effluent dissolved oxygen concentration reaches a predetermined minimum effluent dissolved oxygen concentration. When the oxygenating mechanism includes a timer in electric communication with the air pump or aerator, the timer may actuate the air pump to periodically oxygenate effluent. The oxygenating mechanism may oxygenate the effluent to achieve an effluent oxygen concentration sufficient to support aerobic soil organisms in the absorption field. The absorption field may define one infiltration surface or a plurality of infiltration surfaces proximate the permeable fluid conducting member. The infiltration surfaces, in turn, may define a cavity, such as a trench, accommodating the permeable fluid conducting member. Aggregate may be disposed in the trench and substantially surround the permeable fluid conducting member. A lift station in fluid communication with the impermeable member may be present, e.g., when the absorption field elevation is higher than elevations of upstream portions of the hydraulic system (settling tank).
There is also provided a process for enhancing effluent infiltration capacity of an absorption field. The absorption field may define an infiltrative surface and may receive effluent from a hydraulic system at the infiltrative surface. The hydraulic system may functionally include an anaerobic portion and an anaerobic portion separated at an interface. The anaerobic portion may be characterized by an anaerobic BOD. The aerobic portion may be characterized by an aerobic BOD and may be disposed downstream from the anaerobic portion. The anaerobic BOD may be substantially equal to the aerobic BOD. The process may include 1) dissolving oxygen in the effluent proximate the interface, thereby generating oxygenated effluent; and 2) flowing the oxygenated effluent from the interface to the absorption field infiltrative surface. If a biomat is proximate the infiltrative surface, the process may include aerobically decomposing the biomat. Oxygen may be dissolved in the effluent when the effluent is flowing through the impermeable member, through the permeable member, or proximate a lift station at a location proximate the interface. The amount of oxygen dissolved in the effluent over periods of twelve hours, 24 hours, seven days, fourteen days, 30 days, 60 days, 90 days, or six months may be at least equal to the biomat BOD. The amount of oxygen dissolved in the effluent over the preceding periods may also be at least equal to a BOD mass load exerted by the biomat, the mass load being equal to the BOD concentration entering the infiltrative surface multiplied by the wastewater flow entering the infiltrative surface. In another sense, the oxygen dissolved in the effluent may be sufficient to create an oxygen concentration in the effluent such that an oxidation/reduction potential of at least xe2x88x92250 mV, xe2x88x9275 mV, +120 mV, +220 mV, or +400 mV is generated proximate the infiltrative surface. The oxygen dissolved in the effluent may be sufficient to create a measurable oxygen concentration (greater than zero ppm) at the infiltrative surface. The oxygen dissolved in the effluent over one of the preceding periods may be sufficient to increase the hydraulic conductivity of the soil proximate the interface by at least 0.1 inch per hour. In another aspect a sufficient amount of oxygen may be dissolved to eliminate pondering at the interface over one of the preceding time periods.
One feature of the present system and method is that absorption fields are reclaimed or maintained without reducing the BOD of the effluent being disposed of therein.
Another feature of the present system and method is that absorption fields are reclaimed or maintained without using expensive and maintenance-intensive oxidizers such as hydrogen peroxide or ozone.
Still another feature of the present system and method is that absorption fields are reclaimed or maintained, rather than being replaced.
Yet another feature of the present system and method is that absorption fields are reclaimed or maintained without being idled for an extended period of time.
These and other objects, features, and advantages of this invention will become apparent from the description which follows, when considered in view of the accompanying drawings.